G proteins function as molecular switches They are turned \"on\" by G protein-co
ID: 206377 • Letter: G
Question
G proteins function as molecular switches They are turned "on" by G protein-coupled receptors. What turns them "oft" (deactivates them following receptor activation)? A. CAMP phosphodiesterase. B. Dissociation of neurotransmitter bound to the G protein-linked receptor C. phosphorylation of the receptor D. Intrinsic GTPase activity of the Ga subunit. Trimeric G proteins are signaling molecules A. with an alpha subunit that binds to GTP B. that transform GTP into cyclic GMP C. that are activated by a serine/threonine kinase. D. associated with the outer face of the plasma membrane. Which of the following is often involved in the process of signal transduction? Interactions between receptor and second messenger molecules B. Transport of signal molecules, for example hormones, across the membrane C. Activation of intracellular protein kinases. D. Increased production of carbohydrates in the nucleus Which of the following statements concerning receptor enzymes is FALSE? A. They are usually membrane-associated proteins. B. They have an active site on the extracellular side of the membrane. C. They contain an enzyme activity that acts on the inside of the cell. D. They have a ligand-binding site on the extracellular side of the membrane.Explanation / Answer
1) Option D is correct
Intrinsic GTPase activity of the G subunit is responsible for turning off the G-protein coupled receptors. The G subunit hydrolyses the attached GTP to GDP by its inherent enzymatic activity, allowing it to re-associate with G and starting a new cycle.
2) Option A is the correct answer
Trimeric G proteins are signalling molecules with an alpha subunit that binds to GTP taking the place of GDP and causing a large confomational change in protein leading to its activation. it is found on the cytoplasmic surface of plasma membrane.
3) Option C is the correct answer.
Activation of intracellular protein kinases ia a common response in the cascade reaction in the signal transduction process for causing a proper response to the signal. Second messengers do not have a direct contact with the receptor, rather they are activated by the first messengers. Signal molecules such as hormones usually do not cross the plasma membrane, with the steroid hormones being an exception.
4) Option B is the correct answer.
An enzyme-linked receptor, also known as a catalytic receptor, is a transmembrane receptor, where the binding of an extracellular ligand causes enzymatic activity on the intracellular side.
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